The production of oxygen using vacuum swing adsorption (VSA) is well-known to air separation technologists. VSA offers a simple non-cryogenic method to produce gaseous oxygen at purities of 80% to 95%. In the last 20 years oxygen VSA plants have become widespread and are offered in various bed configurations. The multi-bed VSA is typically used in the size rage of 60 tons per day (TPD) and higher. The single bed process was adopted as a lower capital, simpler process for lower production ranges, typically 1 TPD up to 40 TPD. Typical single bed systems usually consist of a single blower train that is used for both the feed air provider as well as the regeneration vacuum system. The process usually incorporates automatic valves to direct the air and vacuum flows during the cycle. A newer embodiment of the single bed process uses a reversing blower to generate the feed stream and apply vacuum for the regeneration step. This latest embodiment is well suited for small to medium sized oxygen VSA production plants (1 to 10 TPD). One example of a single bed reversing blower (SBRB) VSA process of this type is described in U.S. Pat. No. 8,496,738.
Although the single bed reversing blower (SBRB) VSA process is simple in practice, its simplicity comes with performance trade-offs when compared to multi-bed systems. Firstly, the lack of additional adsorber beds does not allow for a crucial bed to bed equalization. The pressure equalization step is key to lowering power consumption and increasing product oxygen recovery. Technologists in the art have overcome this deficiency by adding an equalization tank to the SBRB system (such as equalization tanks in SBRB systems provided by Air Liquide of Houston, Tex.).
Another problem with single bed reversing blower VSA systems is the inefficiency associated with energy lost as the motor reverses direction. The motor needs to slow down quickly then accelerate in a reverse direction within just a few seconds. Resistive electric breaking is typically used, but this generates significant heat which has no benefit to the VSA system, but rather is merely lost energy. Thus, a need exists for SBRB systems, such as VSA adsorption systems which reverse the blower more efficiently and effectively.